Hydraulic hammer with back pressure isolation

ABSTRACT

An improved hydraulic hammer constructed to eliminate frequency variations in operation due to fluctuating back pressure. A flow path from a hammer operating piston to a fluid outlet is provided with a venturi to isolate the piston from fluctuation in back pressure downstream of the restriction.

' United States Patent Klessig HYDRAULIC HAMMER WITH BACK PRESSUREISOLATION Inventor: Ernst F. Klessig, Racine, Wis.

Assignee: Worthington Corporation (Worthington Compressor and EngineInternational Division), Holyoke, Mass.

Filed: Nov. 9, 1970 Appl. No.: 87,966

[1.8. CI ..l73/l34, 173/17 Int. Cl. ..E2lb 1/00 Field of Search ...l73/134, 17; 91/404, 407, 394

References Cited UNITED STATES PATENTS 2,881,739 4/1959 l-luppert173/134 1 1 Oct. 3, 1972 3,213,615 10/1965 Bjiirnberg ..l73/l34 XFOREIGN PATENTS OR APPLICATIONS 819,486 8/1969 Canada 173/1 34 PrimaryExaminer-David H. Brown Attorney-Hofgren, Wegner, Allen, Stellman & Mc-Cord 5 7] ABSTRACT 6 Claims, 1 Drawing Figure HYDRAULIC HAMMER WITH BACKPRESSURE ISOLATION BACKGROUND OF THE INVENTION Over the years, variousforms of demolition work have been accomplished in part through the useof power hammers. In recent years, after extended research anddevelopment programs, various concerns have developed, for commercialproduction, a type of power hammer that is driven by hydraulic fluidunder pressure. Such hydraulic hammers perform work as efficiently andmore economically than the type of power hammer, specifically an airhammer, previously used most frequently and without the high noise levelattendant the operation of an air hammer.

This principal advantage of a hydraulic hammer has resulted in everincreasing use of the same. However, hydraulic hammer constructionsstill require further improvement of various peripheral facets of theiroperation. For example,; one difficulty common to many existingcommercial hydraulic hammer constructions is the undesirable,uncontrolled variations in the frequency of reciprocation of the hammerelement. Specifically, it is quite typical of hydraulic hammers to drivea piston associated with a hammer in one direction within a housing byapplying fluid under pressure to one side of the piston and connectingthe other side of the piston to a fluid outlet. When variations in backpressure in the fluid flow path extending from the piston to the outletoccur, the resistance opposing the driving of the hammer element variesand the rate at which the hammer element is driven will therefore vary.

One attempted solution to the foregoing problem has been to employ'acheck valve in the'outlet line. To the extent that such a valve willopen when'the pressure differential across the same exceeds apredetermined value, such a valve has been partially successful inalleviatingfrequency variations due to back pressure. However, becausethe valve will open only when a predetermined pressure differentialexists across it, an increased back pressure downstream from the valvewill require a higher pressure upstream of the valve and downstream ofthe piston before the valve will open. Thus,the back pressure applied tothe piston can still vary through a substantial range even with the useof such valves and 'cause variations in operational frequency of thehammer.

SUMMARY OF THE INVENTION application of hydraulic fluid under pressureto one side thereof and through successive return strokes by thecontinuous application of hydraulic fluid under pressure to an opposedsurface on the piston having a lesser size than the first mentionedsurface. During return stroke, the first mentioned surface is connectedto a fluid outlet. Sequencing is provided by a control valve shiftablewithin the hammer casing to connect the first surface to a fluid inletat the beginning of each power stroke and to connect .the first surfaceof the piston to the outlet at the beginning of each return stroke. v

The means for isolating the first surface of the piston from backpressure variations comprises a venturi located downstream of the firstsurface and in the flow path established therebetween and the outletduring the return stroke of the hammer. In the most advantageous form,the venturi is defined by'an annular projector on a spool serving as thecontrol valve, which land is of lesser diameter than a bore in which thespool reciprocates. When the spool is in a position to connect thefirst-mentioned piston surface to the outlet, the projection, inconjunction with the bore in which the spool is received, defines anannular venturi between the first piston surface and the outlet andisolates back pressure variations downstream of the venturi from theflow path connecting with the piston first surface upstream of theventuri.

Other objects and advantages of the invention will become apparent fromthe following specification taken in conjunction with the accompanyingdrawing.

DESCRIPTION OF THE DRAWING The FIGURE illustrates a preferred form of ahydraulic hammer embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT An exemplary embodiment of ahydraulic hammer made according to the invention is illustrated in theFIGURE and is seen to include a casing, generally designated 10, havinga central bore 12 therein. Disposed within the bore 12 for reciprocationtherein is a hammer element, generally designated 14, having an upperend including an annular reduced diameter portion 16 and a pressureresponsive piston 18. The hammer element 14 also includes a lower,enlarged hammer 20 which is disposed within an enlarged diameter portion22 of the bore 12.

Secured to the lower end of the casing 10 is a tool mount 24 having acentral bore 26 receiving a movable tool 28 which is disposed to bestruck by the hammer 20 and which has a lower, work performing end (notshown). Alternatively, that portion of the tool 28 illustrated could bean anvil having its lower end operatively associated with a selectedtool to be used in conjunction with the hammer. For example, thelowerend of such an anvil may ride on the upper end of the tool. Thetool 28 includes a key way 30 and a key 32 which extends through thetool mount 24 and the key way 30 to restrict the movement of the tool 28within the tool mount 24 to the length of the key way 30.

The casing 10 includes an inlet 34 which may be connected to anysuitable source of hydraulic fluid under pressure to serve as 'a sourceof energy for reciprocating the hammer 20 within the casing 10 to impartenergy to the tool 28. In fluid communication with the inlet is aconventional accumulator 36. The casing 10 further includes an outlet 38and a second accumulator 40 in fluid communication with the outlet 38.

A port 42 transverse to the bore 12 in the casing and in fluidcommunication with the inlet 34 is arranged to permit the application offluid under pressure to a lowermost surface 44 of the piston 18 of thehammer element 14. As will be seen, this application of fluid underpressure serves to move the hammer element l4 upwardly in the bore 12for its return stroke. A series of small grooves 45 extend upwardlypartially to the port 46 from the port 42 for purposes to be seen.

A port 46 normally in fluid communication with the port 42 through thebore 12 and reduced diameter portion 16 provides fluid under pressure toa hydraulically operated control valve spool, generally designated 50,which is operative to control the reciprocation of the hammer element 14within the bore [2. The spool 50 includes a reduced diameter portion 52.The spool 50 is shiftable within a bore 54 to a first position(illustrated in the FlGURE) wherein fluid under pressure from the inlet34 passing through the port 42 and the port 46 is fed along the reduceddiameter portion 52 to the upper end of the bore 12 via a conduit 56 incommunication with both the bore 54 and the bore 12 and applied to anupper surface 58 on the piston 18 of the hammer element 14. The surface58 is larger than the surface 44 so that when fluid under pressure isapplied to the former, notwithstanding the fact that fluid underpressure is also applied to the latter, the hammer element 14 will bedriven downwardly to strike the tool 28. a

A second position of the spool 50 within-the bore 54 is one wherein thespool 50 is shifted upwardly from the position shown in the FIGURE andwherein an enlarged lower end 60 blocks off the path of fluid underpressure from the inlet 34 to the upper end of the bore 12 while anenlarged upper end 62, in conjunction with the reduced diameter portion52 permits fluid in the upper end of the bore above the surface 58 toexit to the outlet 38 via a conduit 64. lnterposed between the conduit64 and the outlet 38 and hydraulically prior to the point of connectionof the accumulator 40 to the outlet 38 is a restriction or orifice 65for purposes to be seen. When the spool 50 is in the just-mentionedposition, the fact that the pressure sensitive surface 58 is subjectedto outlet pressure while the pressure sensitive surface 44 is subjectedto inlet pressure will cause the hammer to move upwardly for its returnstroke.

Positioning of the spool 50 is controlled by a differential pin deviceincluding pins 66 at the lowermost end of the spool 50 and pins 68 atthe opposite end thereof. The pins 66 have a lesser efi'ective area thanthe pins 68 and are continuously subjected to inlet pressure. The pins68 are intermittently subjected to inlet pressure dependent upon theposition of the hammer 14 within the bore 12 and when such is the case,the spool 50 will be driven by the pins 68 to the position shown. Whensuch is not the case, the pins 66 will drive the spool 50 upwardly tothe second mentioned position above. For a more detailed statement ofthe operation and specific construction of the differential pin device,reference may be had to US. Letters Patent No. 3,399,602 to Klessig etal., the details of which are herein incorporated by reference.

As mentioned previously, one of the difficulties encountered in theoperation of hydraulic hammers is variations in the frequency ofoperation principally due to varying back pressure. Specifically, therate of return of the hammer element during the return stroke will begenerally dependent upon the ratio of the area of the smaller surface 44and the pressure applied thereto to the area of the larger surface 58and the pressure applied thereto. And since, during return, the lattersurface is subjected only to outlet pressure, an increased back pressurewill cause a slower rate of return than would be the case with little orno back pressure present. Accordingly, the exemplary embodiment of theinvention includes means by which the back pressure against the surface58 during the return stroke of the hammer element 14 is maintainedconstant so that cycling frequency will be constant.

Specifically, a venturi, generally designated 70, is located in the flowpath from the upper endof the bore 12 to the outlet 38 and which isestablished when the valve 50 is in the second position mentioned above.The venturi 70 is carried on the upper end of the reduced diameterportion 52 of the spool 50. The venturi 70 is generally defined by anannular projection having a diameter less than the diameter of the bore54 and greater than that of the reduced diameter portion 52; an upstreamtapered short side 74; and a downstream tapered long side 76. That is,the longitudinal extent of the upstream side 74 of the projection 72 isless than the longitudinal extent of the downstream side 76.

When the spool 50 is moved upwardly to the second mentioned position,the same, in conjunction with a portion 78 of the bore 54 interposedbetween the conduit 56 and the conduit 64 define an annular venturi. Theannular venturi effectively isolates the pressure in the conduit 56 frompressure variations normally encountered in the return conduit 64.

It should be specifically noted that while the exemplary embodimentemploys a venturi on the spool 50, the same could be located at any oneof a variety of downstream points in fluid communication with the outlet38. However, because the casing 10 is generally fonned as a casting andthe various conduits contained therein are frequently defined by bores,the forming of a restriction in one of the conduits would require arather complex machining or casting operation. In contrast, theformation of the venturi 70 on the spool 50 may be accomplishedrelatively easily during the formation of the reduced diameter portion52 thereon.

The exemplary embodiment further includes a bypass conduit 80 whichextends between the inlet 34 and the outlet 38 and which is normallyclosed by a bypass valve, generally designated 82. The bypass valve 82is mounted for reciprocation within a bore 84 in the casing 10. One endof the bore 84 is closed by a plug 86 which serves to position a spring88 in a recess 90 formed in the body of the valve member 82 to bias thevalve member 82 against a seat 92 surrounding the bypass conduit 80.

The bypass valve 82, intermediate its ends, includes a reduced diameterportion 93 which normally permits fluid under pressure to flow from theinlet 34 to the port 42 for use in driving the hammer in the mannermentioned previously. The bypass valve 82 further includes a pair ofpressure responsive surfaces 94 and 96 with the surface 94 being largerthan the surface 96. The recess 90 terminates in a third pressuresensitive surface 98 on the valve 82. The arrangement is such that thecombined areas of the surfaces 96 and 98 is greater than the area of thesurface 94 but the surface 94 is greater in size than the surface 96alone. More particularly, the surfaces 94, 96 and 98 and the spring 88act such that when'inletpressure is applied against the surface 96 andthe surface 94 (as will always be the case) and is applied to thesurface 98 (as will usually be the case) the valve 82 will be in theposition shown. However, when inlet pressure is not applied to thesurface 98, the valve will shift downwardly from the position shown toopen the bypass 80 whereupon fluid under pressure from the inlet 34 willflow directly to the outlet 38 bypassing entirely the control valve 50.As

a result, reciprocation of the hammer element will cease.

the surface 98 via the port 42 and a section 100 of the bore 12interconnectingthe port 42 and a port 102. The bore section 100 is ofslightly greater diameter than the shank of thehammer element 14 but,for-purposes to be seen, is of the same diameter as the diameter of thepiston 18. a

The relief of fluid pressure against the surface 98 so as to permit thevalve 82 to open for bypass purposes is accomplished by means ofa port104 in the bottom of a stationary sleeve 1106 embracing the shank of thehammer element 14. Also-included are a series of small grooves 105extending upwardly a short distance from the port 104 to permit theestablishment of fluid communication to the port 104 through the boresection 100 slightly before the reduced diameter portion moves to theupper boundary of the port 104. A channel 108 is in fluid communicationwith the port 104 and a bore 110 which empties into the hollow center112 of the spool 50. From the hollow center 112, fluid may flow througha radial bore 114 in the uppermost end of the spool 50 to the conduit 64to the outlet 38. The arrangement is such that when the hammer element14 has been driven downwardly past a position wherein it would normallyencounter the tool 28 and not yet has encountered the tool, the side ofthe piston 18 will enter the bore portion 100 thereby blocking fluidcommunication between the inlet 34 via the port 42 to the surface 98.Simultaneously, the reduced diameter portion 16 on the hammer element 14will establish fluid communication between the port 102 and the port 104thereby permitting the fluid under pressure bearing against the surface98 to flow to the outlet 38 via the path mentioned previously.

This relieving of the pressure against the surface 98 will cause theinlet pressure to shift the valve 82 downwardly thereby permitting fluidfrom the inlet 34 to flow directly to the outlet 38 via the bypass 80without operating the control valve thereby ceasing the reciprocation ofthe hammer 14. As a result, it will be seen that whenever the tool is ata predetermined position within its bore 26 and lower than the desiredposition, as for example, when a tool associated with the anvil 28 isnot bearing against the work, the hammer will automatically cease tooperate.

From the foregoing, it will be seen that a hydraulic hammer madeaccording to the invention employing the venturi can be used in ahydraulic system wherein there are large variations in back pressurewithout affecting the rate of reciprocation of the hammer element duringoperation thereof. The flow characteristics Fluid under pressure fromthe inlet 34 is applied to i of the hydraulic fluid around the venturiare such that pressure variations downstream of the same are effectivelyisolated from the flow path above the venturi so that a constant backpressure will be applied to the piston during the return stroke thereofresulting in a constant rate of operation.

1 claim 1. A hydraulic hammer comprising:

a. a casing having a bore;

b. a hammer received within said bore for reciprocating movementtherein;

c. a work performing member operatively associated with said casing tobe struck by said hammer during reciprocation of said hammer;

(1. means for reciprocating said hammer within said bore including l.means within said bore having opposed first and second pressuresurfaces, said first surface being of greater size than said secondsurface,

2. first means establishing constant fluid communication between saidsecond surface and a source of hydraulic fluid under pressure, and

3. second means alternately establishing fluid communication betweensaid first surface and said source or a hydraulic fluid outlet; and

. means associated with one of said second means and said fluid outletdefining a venturi to maintain back pressure against said first surfaceat a relatively constant level when said second means establishes fluidcommunication between said first surface and said fluid outlet.

2. The hydraulic hammer of claim 1 wherein said second means comprises acontrol valve and said venturi defining means is carried thereon.

3. The hydraulic hammer of claim 1 wherein said second means comprises abore and a reciprocably movable valve spool having a reduced diameterportion received in the bore, and said venturi defining means comprisesa land on said spool reduced diameter portion and having a diameter lessthan the diameter of said bore.

4. A hydraulic hammer comprising:

a. a casing having a bore;

b. a hammer received within said bore for reciprocating movementtherein;

c. a work performing member operatively associated with said casing tobe struck by said hammer during reciprocation of said hammer;

d. means for reciprocating said hammer within said bore including 1.means for driving said hammer in one direction within said bore,

2. means, including a surface to be subjected to hydraulic fluid underpressure, for driving said hammer within said bore in a directionopposite said one direction, and

3. means for. alternately establishing a first fluid flow path betweensaid surface and a source of hydraulic fluid under pressure and a secondflow path between said surface and a hydraulic fluid outlet; and

e. means defining a venturi in said second flow path for isolatingpressure fluctuations downstream of the isolating means from fluid insaid second flow path and upstream of the isolating means whereby borein the casing adjacent said first surface and with 10 said fluid outlet,and a valve spool having a reduced diameter portion received within saidsecond bore for reciprocal movement therein to interconnect said fluidoutlet and said casing bore end in one position of movement within saidsecond bore; and said venturi defining means comprises an annularprojection on said reduced diameter portion having a lesser diameterthan the diameter of said second bore.

6. A hydraulic hammer according to claim 5 wherein the sides of saidprojection are tapered with the side of said projection adjacent saidoutlet having a greater longitudinal extent than the opposite side ofsaid land.

1. A hydraulic hammer comprising: a. a casing having a bore; b. a hammerreceived within said bore for reciprocating movement therein; c. a workperforming member operatively associated with said casing to be struckby said hammer during reciprocation of said hammer; d. means forreciprocating said hammer within said bore including
 1. means withinsaid bore having opposed first and second pressure surfaces, said firstsurface being of greater size than said second surface,
 2. first meansestablishing constant fluid communication between said second surfaceand a source of hydraulic fluid under pressure, and
 3. second meansalternately establishing fluid communication between said first surfaceand said source or a hydraulic fluid outlet; and e. means associatedwith one of said second means and said fluid outlet defining a venturito maintain back pressure against said first surface at a relativelyconstant level when said second means establishes fluid communicationbetween said first surface and said fluid outlet.
 2. first meansestablishing constant fluid communication between said second surfaceand a source of hydraulic fluid under pressure, and
 2. The hydraulichammer of claim 1 wherein said second means comprises a control valveand said venturi defining means is carried thereon.
 2. means, includinga surface to be subjected to hydraulic fluid under pressure, for drivingsaid hammer within said bore in a direction opposite said one direction,and
 3. means for alternately establishing a first fluid flow pathbetween said sUrface and a source of hydraulic fluid under pressure anda second flow path between said surface and a hydraulic fluid outlet;and e. means defining a venturi in said second flow path for isolatingpressure fluctuations downstream of the isolating means from fluid insaid second flow path and upstream of the isolating means wherebypressure against said surface is maintained constant when said secondflow path is established to eliminate variations of operationalfrequency due to said pressure fluctuations.
 3. The hydraulic hammer ofclaim 1 wherein said second means comprises a bore and a reciprocablymovable valve spool having a reduced diameter portion received in thebore, and said venturi defining means comprises a land on said spoolreduced diameter portion and having a diameter less than the diameter ofsaid bore.
 3. second means alternately establishing fluid communicationbetween said first surface and said source or a hydraulic fluid outlet;and e. means associated with one of said second means and said fluidoutlet defining a venturi to maintain back pressure against said firstsurface at a relatively constant level when said second meansestablishes fluid communication between said first surface and saidfluid outlet.
 4. A hydraulic hammer comprising: a. a casing having abore; b. a hammer received within said bore for reciprocating movementtherein; c. a work performing member operatively associated with saidcasing to be struck by said hammer during reciprocation of said hammer;d. means for reciprocating said hammer within said bore including
 5. Ahydraulic hammer according to claim 4 wherein said hammer is arranged tobe driven against said member when said first surface is in fluidcommunication with said source; said second means includes a second borein fluid communication with the end of the bore in the casing adjacentsaid first surface and with said fluid outlet, and a valve spool havinga reduced diameter portion received within said second bore forreciprocal movement therein to interconnect said fluid outlet and saidcasing bore end in one position of movement within said second bore; andsaid venturi defining means comprises an annular projection on saidreduced diameter portion having a lesser diameter than the diameter ofsaid second bore.
 6. A hydraulic hammer according to claim 5 wherein thesides of said projection are tapered with the side of said projectionadjacent said outlet having a greater longitudinal extent than theopposite side of said land.